Recycling waste materials, such as production rejects or finished products that are no longer needed, has assumed increasingly greater importance for environmental and cost reasons. Various processes have been proposed for recycling such waste materials, optionally after suitable treatment, for reuse in making similar or completely different products.
DE 40 26 786 describes a process for recycling granulated, used or waste, fiber-reinforced, cross-linked, thermosetting synthetic resins. EP 0 471 658 (U.S. Pat. No. 5,221,708) describes the use of recovered polyvinyl butyral (PVB) for making floor coverings.
In the printing industry, the use of photopolymer printing plates, especially flexographic printing plates, generates polymer waste.
Raw flexographic photopolymer plates comprise a recording layer, a support, and optionally a cover element. The recording layer is a photopolymerizable material, comprising an elastomeric binder, an unsaturated monomer, and an initiator. The chemical composition of single or multiple recording layers is described, for example, in DE 22 15 090 or EP 0 469 307 (U.S. Pat. No. 5,210,004). A transparent sheet, such as for example, a polyester sheet having a thickness of 0.1 mm to 0.2 mm, is used as a support. A flexible transparent polymeric sheet is used as a cover element.
To transfer image information onto the raw plate, the recording layer is exposed to actinic light through a negative in an exposure apparatus. Polymerization changes the physical properties of the exposed areas of the recording layer. Exposed areas are insoluble in a washoff solvent, whereas unexposed areas are dissolved by the solvent and removed in the washoff process, yielding a relief image. Thus, the raw plate has been converted to a photopolymer printing form or for short, a printing form.
Photopolymer materials that are considered waste by one skilled in the art, are unexposed material that are leftover from the manufacture of photopolymerizable raw plates. Such wastes would include for example, (a) edge strips, (b) losses from starting and stopping production, and (c) unusable, out-of-date raw plates. Large quantities of waste from exposed printing plates accumulate in printing plants as plates that are no longer needed. Such wastes are currently either burned or following exposure to ultraviolet radiation, are deposited in waste dumps.
It is becoming clear, especially in the disposal of raw plate wastes, that this problem is not being handled satisfactorily. Unused, valuable material containing mostly unexposed photopolymer is disposed of by expensive and environmentally unfriendly processes.
Therefore, a problem addressed in the present invention is the formulation of a process for recycling the unexposed photopolymerizable and the exposed photopolymerized components of flexographic printing plates. Another problem addressed in the present invention is the formulation of photopolymer flexographic printing plates and processes for their production, which (a) reduce waste problems, (b) place a smaller burden on the environment, and (c) require less raw materials.
These problems are solved by the present invention.